Structure-directed electrochemical enhancement of hydrothermally grown quaternary NiCoCuZnO electrodes for energy storage applications

The structural and electrochemical characteristics of multicomponent transition metal oxides are profoundly influenced by compositional variation, providing an effective route to enhance energy storage capabilities. In this study, the quaternary oxide system NiCoCuZnO was systematically engineered by adjusting the Cu and Zn contents to explore their impact on structure and supercapacitor performance. The quaternary electrode materials were synthesized on stainless steel (SS) mesh substrates via a one pot hydrothermal process. The optimized Cu/Zn composition exhibited superior electrochemical kinetics, enhanced redox activity, and improved electronic conductivity due to synergistic cationic interactions within the spinel lattice. XPS reveals that controlled Cu/Zn incorporation induces electronic structure modulation and defect generation within the multicomponent oxide, leading to a higher proportion of redox-active Ni 3+ /Co 3+ species and oxygen vacancies. The FE-SEM revels that the impact of Cu and Zn concentrations led to notable modifications in the morphology and microstructural evolution of the quaternary oxide. These structural adjustments played a vital role in governing charge transfer efficiency and ion diffusion behavior in the active sites. Furthermore, while TEM analyses confirmed well-defined nanostructures with clear lattice fringes and good crystallinity. The SAED pattern further verified the polycrystalline nature of the material. The electrochemical evaluation revealed that the quaternary electrode with a metal precursor ratio in molar of 4:3:2.5:0.5 (Ni:Co:Cu:Zn) delivered the highest specific capacitance of 761.67 F/g at 1 mA/cm 2 current density and retained 87% of its capacitance after 7000 charge-discharge cycles at 10 mA/cm 2 . Furthermore, a symmetric NCCZ//NCCZ energy storage supercapacitor device assembled using this optimized electrode achieved a specific capacitance of 23.37 F/g at 5 mA/cm 2 , corresponding to an energy density of 10.52 Wh/kg and a power density of 1386.74 W/kg, maintaining 66.7% capacitance retention over 5000 cycles. The study highlights the improved electrochemical performance is attributed to the synergistic interaction among Ni, Co, Cu, and Zn ions, which modulates the electronic structure and enhances the redox-active sites within the oxide matrix. In particular, the simultaneous tuning of Cu and Zn composition plays a crucial role in optimizing defect density, electrical conductivity, and ion diffusion pathways, leading to enhanced charge storage behavior.